There has been a big change in our lawns in the past week. The soil temperatures are finally warming up enough that the grass is close to complete green-up. The recent rain also helped wash away the pollen and is helping the grass grow.
There are some disease problems that are starting to show up in our lawns that can be associated with our management of the turf.
Improper fertilization can lead to disease problems. When too much fertilizer is applied, the fungi use the excess nitrogen to build their numbers and will start to attack the grass.
Watering too often and at the wrong time can lead to disease problems as well. Lawns should be watered deeply and less often to be healthy.
The other factor associated with disease problems is thatch, an accumulation of dead and living plant material that develops between the soil surface and the green leaves of a turf. Thatch development is a natural process that occurs during normal growth of turfgrasses, but over-fertilization and improper watering can speed the accumulation of thatch.
The leaves of grass do not add to thatch if the turf is being mowed, fertilized and watered properly. Grass clippings can be left on a properly managed lawn. Although some thatch is desirable, it becomes undesirable when it exceeds a depth of 1/2 inch. When thatch is deeper than that, it provides a home for insects, fungi and restricts the movement of water, fertilizer and pesticides to the root-system of the turf.
To determine if turf has a thatch problem, take a sample of the turf with soil included. The thatch layer is on top of the soil, and should be reduced if there is a problem. Thatch takes a number of years to build up, so it will take a number of years to reduce it.
There are several ways to reduce the thatch layer. The first way is by topdressing by applying a quarter inch of soil over the lawn. This needs to be done twice a year until the problem is corrected.
The best soil to use is a good quality topsoil or a good man-made topsoil. These soils have microorganisms in them that help in the decomposition of thatch. Many people use sand as a top-dressing, but this is not recommended because sand doesn't aid in decomposition. Also, sand doesn't hold moisture or nutrients.
There are some sand mixes on the market that is a combination of sand and compost. This can be used because the compost has the micro-organisms that aid in decomposition. If too much top-dressing is applied at one time, it can cause a layer of soils that can reduce the amount of air, water and nutrients to the grass roots.
Another way to reduce thatch is by vertical mowing. This mower has evenly spaced blades that revolve perpendicular to the turf and slice into the thatch to mechanically remove it. Vertical mowing is best done in the spring after green-up where the grass is growing rapidly and when the weather is not so hot that turf water needs are high. Another good time to vertical mow is in early spring just before green-up occurs.
Vertical mowing also can be done in the fall if the lawn is over-seeded. A blade spacing of 1 to 2 inches should be used for Bermuda and zoysia grasses. These grasses may be mowed down to the soil level in several directions without killing the lawn because of underground rhizomes.
Power raking is another method. Power raking uses the same mechanical principles as vertical mowing. Power rakes have flexible spring steel wires that revolve at high speed vertically through the turf and loosen the debris for removal. Power raking is not as effective as vertical mowing.
Another method is core aeration, which benefits thatch decomposition primarily through the indirect effects that stimulate bacterial activity. Core aeration also relieves soil compaction and increases air and water movement into the soil. This is best accomplished by a power aerator with hollow tines or spoons, so it removes a soil core 2 to 3 inches deep.
Core aeration should be done during periods of active growth and when the soil is moist enough to allow deep penetration. Applying a fertilizer as recommended by soil analysis will increase the rate of turf recovery.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@ comcast.net.
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